Process for staining concrete



' concrete surfaces.

Patented July 3,1945

UNITED STATES I 2,379,502 PROCESS FOR STAINING CONCRETE Ernest H. Swift,Pasadena, Calif,

No Drawing. Application August 10, 1942, Serial No. 454,296

Claims. (Cl. 111-123) This invention relates to a process of and meansfor staining concrete.

The object of my invention is to provide a process of and means forstaining concrete without a preliminary acid treatment to the surface 5of the concrete.

Another object of my invention is to provide a simplified process andmeans for staining concrete in which the cost of the process is veryeconomical, in which the intensity of the color is increased, and inwhich the staining chemicals penetrate more deeply into the surface,thus producing a more durable stain. .1

Another object of my invention is to provide a process of stainingconcrete in which the stain- 16 ing solutionis buffered to a pH ofdefinite value in order to obtain uniformity of color with a concretesurface which may vary in alkalinity.

Other objects and advantages of my invention will be evident from theexamples of my inven- 20 tion set forth hereinafter.

Heretofore it has been .common practice to employ the metallic sulfatesin preparing solutions for the staining of concrete surfaces; cupricsulfate, manganous sulfate, ferrous sulfate, also ferric, aluminum andchrome alums have been commonly specified. These salts have been usedbecause of their cheapness and commercial availability. However,sulfates have certain undesirable features. It is desirable that thesolutions used for the staining process be quite concentrated (in orderto secure better penetration and intensity of the stain). However, thesulfates in general are not as soluble as are certain other salts, suchas the chlorides, nitrates and acetates. Also, the limited solubility ofthe sulfates has made it necessary to mix the solutions at the locationof the staining operation in order to avoid transporting large volumes-of such solutions. Finally, the sulfate radicle, or anion, has theundesirable property of forming insoluble calcium sulfate with thecalcium cation. The formation of this insoluble calcium sulfate hasheretofore caused two defects in the chemical staining of First, theexcess of lime in and on the surface of concrete structures, has causedit to be necessary to make a preliminary treatment of thesurface of theconcrete to be stained with an acid, such as a dilute solution ofhydrochloric acid, in order to dissolve and remove this lime and thus toavoid the formation of an excessive amount of an adherent surface filmof calcium sulfate. Secondly, the formation of insoluble calcium sulfatein the surface la ers of the concrete has prevented the penetration ofthe staining chemicals into the concrete to produce the permanent anddurable stains as is desired. 1

I have found that if the staining solutions are composed of compoundscontaining only those anions which form, with the constituents of thesolution, salts which. are extremely, soluble in watenand if,furthermore, these solutions contain only anions which form very solublesalts with calcium, for examples, chlorides, acetates, or nitrates, theprocess of applying the stain can be much simplified, the cost of theprocess materially reduced, the intensity of the color can be increased,and the staining chemicals caused to penetrate more deeply into thesurface thus pro-. ducing a more durable stain. In fact, thesimpiiflcation of the process resulting from the use of such solutionsnow makes it possible to sell such solutions to the untrained layman andfor such layman to'successfully apply the stain without previoustraining in the art. Thus with such solutions it is now possible toobtain by a simple application of the solution to the surface of theconcrete a more intense stain than was heretofore obtained by the use ofa preliminary acid treatment followed by three successive applicationsof the former staining solutions.

, As an example, I have found that a solution of the followingproportions by weight produces a penetrating and intense reddish browncolor on concrete: a

v Parts Ferric chloride 2 Ammonium chloride 1 Water 5 The surface of theconcrete to be stained is first cleaned, after which the stainingsolution may be applied directly to the surface by means 01' a brush ora spray gun, or by simply flooding the surface of the concrete with thesolution,

without any preliminary acid treatment whatever. In connection with theabove example, I have produced satisfactory stains by using 3.3 poundsof solution per square feet, although more or less of the solution maybe used depending upon the intensity and penetration desired and uponthe composition, texture, and age of the concrete to be stained.

Although a stain can be produced by a solution consisting of 2 parts offerric chloride and 5 parts of water, the results are not entirelysatisfactory for several reasons. The addition ofthe ammonium chlorideincreases the penetration and intensity of the stain. This effect is tobe attributed to the fact that ferric chloride forms with an excess ofchloride ion the complex tetrachlorferriate anion, thus decreasing thehydrolysis and increasing the solubility of the ferric chloride andpermitting a deeper penetration of the concrete before decomposition tothe hydrous oxide takes place.

I have found that a solution of the following proportions by weightproduces a. penetrating and dark brown stain on concrete:

Chromic nitrate 2 Sodium dichromate. 1 Water 6 and that a pleasinggreenish tan color can be obtained by the use of a solution of thefollowing proportions by weight:

Chromic nitrate 6 Sodium chromate 3 Acetic acid (glacial) 1 Sodiumacetate 3 Water 15 The sodium acetate and acetic acid are advantageouslyused where it is desired to buffer the solution to a pH of definite:value and thus obtain uniformity of color with a concrete surface whichvaries in its alkalinity. 7

These solutions are applied in the same man- .ner and in approximatelythe same amounts as set forth above in connection with the ferricchloride solution.

From the foregoing description, the uses, advantages, and operation ofmy invention will be readily understood by those skilled in the art towhich the invention appertains. While I have described certain examplesof my invention, I desire to have it understood that the examples 'givenare merely illustrative, and thatthe invenof forming soluble calciumsalts, and containing sodium acetate and acetic acid to buffer thesolution to compensate for variations in alkalinity of the surface ofthe concrete in order to obtain uniformity of color with a concretesurface which varies in its alkalinity.

, 2. The process of staining concrete without a preliminary acidtreatment to the surface of the concrete which comprises applying aconcentrated solution of staining chemicals which act by depositingmetallic oxide directly to the surface of the concrete, said chemicalscontaining as anions only those radicals capable of forming solublecalcium salts, and containing an acid and a salt of that acid to bufferthe solution in order to obtain uniformity of color with a concretesurface which varies in its alkalinity,

3. In a single step process for staining concrete having a film ofcalcium salt thereon, the improvement comprising applying directly tothe concrete surface a concentrated solution of an iron salt containingas anions only those radicals which form calcium salts that areextremely soluble in water, and containing an acid and a salt of thatacid to buffer the solution in order to obtain uniformity of color witha concrete surface which varies in its alkalinity.

4. The single step process of staining concrete without a preliminaryacid treatment of the surface of the concrete, which comprises applyingdirectly to the surface of the concrete, a concentrated solution of amanganese salt containing as anions only those radicals which formcalcium salts which are soluble in water, and containing an acid and asalt of that acid to buffer the solution so as to obtain uniformity ofcolor with a concrete surface which varies in its alkalinity.

5. In a single step process of staining concrete 0 without preliminaryacid treatment of the same,

.the improvement comprising applying directly to the untreated concretesurface a concentrated solution of a copper salt containing as anionsonly those radicals which form calcium salts that are soluble in water,and containing an acid and a salt of that acid to buffer the solutionand obtain uniformity of color on a concrete surface which varies in itsalkalinity at different points.

ERNEST H. SWIFI'.

